Câu 1:71+(26-3x):5=75

=>(26-3x):5=75-71

=>26-3x=4*5

=>3x=26-20

=>x=6:3

=>x=2

Câu 2:3636:(12x-91)=36

=>12x-91=3636:36

=>12x=101+91

=>x=192:12

=>x=16

Câu 1 :\(71+\left(26-3xX\right):5=75\)

\(\left(26-3xX\right):5=75-71\)

\(\left(26-3xX\right):5=4\)

\(26-3xX=4x5\)

\(26-3xX=20\)

\(3xX=26-20\)

\(3xX=6\)

\(X=6:3\)

\(X=2\)

Câu 2 : \(3636:\left(12xX-91\right)=36\)

\(12xX-91=101\)

\(12xX=101+91\)

\(12xX=192\)

\(X=192:12\)

\(X=16\)

Câu 1:

\(71+\left(26-3x\right):5=75\)

\(\left(26-3x\right):5=75-71\)

\(\left(26-3x\right):5=4\)

\(26-3x=4\times5\)

\(26-3x=20\)

\(3x=26-20\)

\(3x=6\)

\(x=6:3\)

\(x=2\)

Câu 2:

\(3636:\left(12x-91\right)=36\)

\(12x-91=3636:36\)

\(12x-91=101\)

\(12x=101+91\)

\(12x=192\)

\(x=192:12\)

\(x=16\)

a)(9x+2)x3=60

        9x+2 =60:3

        9x+2  =20

              9x =20-2

              9x=18

                x=18:9

                 x=2

a,x=2

b,x=2

c,x=9

o phan a 

(9x+2)*3=60

9x+2=20

9x=18

x=2

o phan b

71+(26-3x)/5=75

(26-3x)/5=75-71=4

26-3x=4*5=20

3x=26-20=6

x=6/3=2

vay x=2

o phan c 

(x-6)^2=9

(x-6)^2=3^2

=>x-6=3

=>x=9

vay x =9

ở phần d 

1+3+.....+x=465

=>(x+1)*(x-1)/2+(x+1)=465

=>(x+1)*(x-1)/2

d) Ta có: \(32\%-0.25:x=-\dfrac{17}{5}\)

\(\Leftrightarrow0.25:x=\dfrac{8}{25}+\dfrac{17}{5}=\dfrac{93}{25}\)

hay \(x=\dfrac{25}{372}\)

Vậy: \(x=\dfrac{25}{372}\)

e) Ta có: \(\left(x+\dfrac{1}{5}\right)^2+\dfrac{17}{25}=\dfrac{26}{25}\)

\(\Leftrightarrow\left(x+\dfrac{1}{5}\right)^2=\dfrac{9}{25}\)

\(\Leftrightarrow\left[{}\begin{matrix}x+\dfrac{1}{5}=\dfrac{3}{5}\\x+\dfrac{1}{5}=-\dfrac{3}{5}\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{2}{5}\\x=-\dfrac{4}{5}\end{matrix}\right.\)

Vậy: \(x\in\left\{\dfrac{2}{5};-\dfrac{4}{5}\right\}\)

f) Ta có: \(-\dfrac{32}{27}-\left(3x-\dfrac{7}{9}\right)^3=-\dfrac{24}{27}\)

\(\Leftrightarrow\left(3x-\dfrac{7}{9}\right)^3=\dfrac{-8}{27}\)

\(\Leftrightarrow3x-\dfrac{7}{9}=-\dfrac{2}{3}\)

\(\Leftrightarrow3x=\dfrac{1}{9}\)

hay \(x=\dfrac{1}{27}\)

g) Ta có: \(60\%\cdot x+0.4x+x:3=2\)

\(\Leftrightarrow\dfrac{4}{3}x=2\)

hay \(x=\dfrac{3}{2}\)

Vậy: \(x=\dfrac{3}{2}\)

h) PT \(\Leftrightarrow\left|\dfrac{20}{9}-x\right|=\dfrac{2}{9}\) \(\Rightarrow\left[{}\begin{matrix}\dfrac{20}{9}-x=\dfrac{2}{9}\\x-\dfrac{20}{9}=\dfrac{2}{9}\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x=2\\x=\dfrac{22}{9}\end{matrix}\right.\)

  Vậy ...

i) PT \(\Leftrightarrow\dfrac{8}{5}+\dfrac{2}{5}x=\dfrac{16}{5}\) \(\Leftrightarrow\dfrac{2}{5}x=\dfrac{8}{5}\) \(\Leftrightarrow x=4\)

  Vậy ...

Bài 3 :

Câu a : \(2x\left(12x-5\right)-8x\left(3x-1\right)=30\)

\(\Leftrightarrow24x^2-10x-24x^2+8x=30\)

\(\Leftrightarrow-2x=30\)

\(\Leftrightarrow x=-15\)

Vậy \(x=-15\)

Câu b : \(3x\left(3-2x\right)+6x\left(x-1\right)=15\)

\(\Leftrightarrow9x-6x^2+6x^2-6x=15\)

\(\Leftrightarrow3x=15\)

\(\Leftrightarrow x=5\)

Vậy \(x=5\)

Bài 4 : Ta có :

\(x\left(3x+12\right)-\left(7x-20\right)-x^2\left(2x+3\right)+x\left(2x^2-5\right)\)

\(=3x^2+12x-7x+20-2x^3-3x^2+2x^3-5x\)

\(=20\)

Vậy biểu thức ko phụ thuộc vào biến !

Bài 5 : Ta có :

\(A=x^5-70x^4-70x^3-70x^2-70x+34\)

\(=x^5-\left(71-1\right)x^4-\left(71-1\right)x^3-\left(71-1\right)x^2-\left(71-1\right)x+34\)

\(=x^5-\left(x-1\right)x^4-\left(x-1\right)x^3-\left(x-1\right)x^2-\left(x-1\right)x+34\)

\(=x^5-x^5+x^4-x^4+x^3-x^3+x^2-x^2+x+34\)

\(=x+34=71+34=105\)

Vậy \(A=105\)

a) \(2\left(3x-4\right)=18\Leftrightarrow3x-4=9\)

\(\Leftrightarrow3x=13\Rightarrow x=\frac{13}{3}\)

b) \(\left(105-x\right)\div25=30+1\)

\(\Leftrightarrow105-x=775\)

\(\Leftrightarrow x=-670\)

c) \(2x-138=22.32\)

\(\Leftrightarrow x-69=11.32\)

\(\Leftrightarrow x-69=352\)

\(\Rightarrow x=421\)

d) \(\left(6x-9\right).28=5628\)

\(\Leftrightarrow\left(2x-3\right).84=5628\)

\(\Leftrightarrow2x-3=67\)

\(\Leftrightarrow2x=70\)

\(\Rightarrow x=35\)

e) \(\left(9x+2\right).3=60\)

\(\Leftrightarrow9x+2=20\)

\(\Leftrightarrow9x=18\)

\(\Rightarrow x=2\)

g) \(\left(26-3x\right)\div5+71=75\)\(\Leftrightarrow26-3x=20\)

\(\Leftrightarrow3x=6\)

\(\Rightarrow x=2\)

h) \(5x+1=125\)

\(\Leftrightarrow5x=124\)

\(\Rightarrow x=\frac{124}{5}\)

i) \(\left(x-5\right)\left(2x+8\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}x-5=0\\2x+8=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=5\\2x=-8\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=5\\x=-4\end{cases}}\)

a) 2 ( 3x - 4 ) = 18

<=> 3x - 4     = 9

<=> 3x          = 13

<=> x            = \(\frac{13}{3}\)

b) ( 105 - x ) : 25 = 30 + 1

<=> ( 105 - x ) : 25 = 31

<=> 105 - x        = 775

<=> x                 = -670

c) 2x - 138 = 22 . 32

<=> 2x - 138 = 704

<=> 2x          = 842

<=> x            = 421

a) 2 (3x - 4) = 18

          3x - 4 = 18 : 2

          3x - 4 = 9

                3x = 9 + 4

                3x = 13

                  x =\(\frac{13}{3}\)

b) (105 - x) : 25 = 30 + 1

    (105 - x) : 25 = 31

              105 - x = 31 . 25

               105 - x = 775

                   => x = -670

c) 2x - 138 = 22 . 32

    2x - 138 = 704

              2x = 704 + 138

              2x = 842

                x = 842 : 2

                x = 421

d) (6x - 39) . 28 = 5628

              6x - 39 = 5628 : 28

              6x - 39 = 201

                      6x = 201 + 39

                      6x = 240

                        x = 40

e) (9x + 2) . 3 = 60

             9x + 2 = 60 : 3

             9x + 2 = 20

                   9x = 20 - 2

                    9x = 18

                      x = 18 : 2

                      x = 9

g) (26 - 3x) : 5 + 71 = 75

             (26 - 3x) : 5 = 75 - 71

              (26 - 3x) : 5 = 4

                     26 - 3x = 4 . 5

                     26 - 3x = 20

                            3x = 26 - 20

                            3x = 6

                              x = 6 : 3

                               x = 2

h) 5x + 1 = 125

           5x = 125 - 1

           5x = 124

             x = 124 : 5

             x =\(\frac{124}{5}\)= 24,8

i) (x - 5) (2x + 8) = 0

 \(\Rightarrow\orbr{\begin{cases}x-5=0\\2x+8=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=5\\2x=-8\end{cases}\Leftrightarrow}}\orbr{\begin{cases}x=5\\x=-4\end{cases}}\)

Sai thì thôi~

#Học tốt!!!

~NTTH~

a) Ta có: \(71+\frac{26-3x}{5}=75\)

\(\Leftrightarrow\frac{26-3x}{5}=4\)

\(\Leftrightarrow26-3x=20\)

\(\Leftrightarrow3x=6\)

hay x=2

Vậy: x=2

b) Ta có: \(\left|x-12\right|=5\)

\(\Leftrightarrow\left[{}\begin{matrix}x-12=5\\x-12=-5\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=17\\x=-5+12=7\end{matrix}\right.\)

Vậy: \(x\in\left\{17;7\right\}\)

c) Ta có: \(\frac{7}{8}+x=\frac{3}{5}\)

\(\Leftrightarrow x=\frac{3}{5}-\frac{7}{8}\)

\(\Leftrightarrow x=\frac{24}{40}-\frac{35}{40}\)

hay \(x=-\frac{11}{40}\)

Vậy: \(x=-\frac{11}{40}\)

d) Ta có: \(\frac{1}{2}x-\frac{2}{5}=\frac{1}{5}\)

\(\Leftrightarrow\frac{1}{2}\cdot x=\frac{1}{5}+\frac{2}{5}=\frac{3}{5}\)

\(\Leftrightarrow x=\frac{3}{5}:\frac{1}{2}=\frac{3}{5}\cdot2\)

hay \(x=\frac{6}{5}\)

Vậy: \(x=\frac{6}{5}\)

hết cứu

Lời giải:
a.

$(x-15).27=0$

$x-15=0:27=0$

$x=15+0=15$

b.

$23(42-x)=0$

$42-x=0$

$x=42$

c.

$(9x+2).3=60$

$9x+2=60:3=20$

$9x=18$

$x=2$
d.

$71+(26-3x):5=75$

$(26-3x):5=75-71=4$

$26-3x=4.5=20$

$3x=26-20=6$

$x=6:2=3$